1. Field of the Invention
The present invention relates to a device for detecting a position designated by a position designating magnetic generator on the basis of change in magnetic permeability of a magnetic substance to which a magnetic field is applied by the position designating magnetic generator.
2. Description of the Prior Art
A conventional position detecting device detects a position which is indicated by a position indicating pen in the following way. A pulse current is applied to one end of a magnetostrictive transmittance medium or to the tip of a position indicating pen in order to produce magnetostrictive oscillating waves on the magnetostrictive transmittance medium, and the time required for the voltage induced by the magnetostrictive oscillating waves to be detected on a detection coil which is provided on the tip of the position indicating pen or one end of magnetostrictive transmittance medium is measured by a processing unit or the like, so that the position of the position indicating pen may be obtained by calculation. Such a device is comparatively good in detecting accuracy but the fact that a cord is required between the pen and the device for delivery of a timing signal and the like between the pen and the processing unit and the like brings about various problems. For example, the operability of the pen is greatly limited; the device is likely to be influenced by induction from other mechanisms, thereby causing errors; the pen may be a source of noise generation; and the pen must be held perpendicular to the magnetostrictive transmittance medium and brought into close proximity thereto during operation.
In another conventional position detecting device, a plurality of driving lines and detecting lines is arranged orthogonal to each other, a current is applied to the driving lines subsequently, and the induced voltage is detected by subsequently selecting the detecting lines, so that the position designated by a position indicating pen having a magnetic member such as ferrite is detected from the position of a detecting line on which a large voltage has been induced. This device dispenses with the need for the position indicating pen to be provided with a cord. However, the resolving power of the ordinate position is determined by the spacing between the lines, and if the spacing is reduced as a means of enhancing the resolving power, the SN ratio and stability are degenerated or, in other words, it is difficult to improve the resolving power. Further, it is difficult to detect a position directly over the intersecting points of the driving lines and the detecting lines. Since the position indicating pen must be used in close proximity to the lines, nothing thick is allowed to be placed on the input surface during use.
In addition, both the above-described position detecting devices, which use a coil, have limitations with respect to the potential for reducing the thickness of the tablet portion.